Many vehicles currently in use do not provide structural enclosure for the operator and passengers. Thus, the operator and passengers of vehicles such as motorcycles, three-wheel and four-wheel all terrain vehicles, jet skis and other vehicles are potentially subject to more severe injury particularly to the head and neck areas as a result of crashes or collisions of the vehicles, especially if the speeds involved tend to throw the operator and passengers off or out of the vehicle.
While it is often required that safety helmets be worn by all persons riding such vehicles it has been found that safety helmets although protecting against head injury in accidents may contribute to more severe neck injuries.